He blessed a well called Slane, located to the west of Magh Tuireadh and east of Loch Arboch in a place called the Field of the Apple Tree (Achad Abla),[4] where the Tuatha Dé could bathe when wounded; they became healed and continued fighting. It would heal any wound but decapitation.[3]

It was Dian Cecht who once saved Ireland, and was indirectly the cause of the name of the River Barrow.[5][6] The Morrígú, the heaven-god's fierce wife, had borne a son of such terrible aspect that the physician of the gods, foreseeing danger, counselled that he should be destroyed in his infancy.[6] This was done; and Dian Cecht opened the infant's heart, and found within it three serpents, capable, when they grew to full size, of depopulating Ireland.[6] He lost no time in destroying these serpents also, and burning them into ashes, to avoid the evil which even their dead bodies might do.[6] More than this, he flung the ashes into the nearest river, for he feared that there might be danger even in them; and, indeed, so venomous were they that the river boiled up and slew every living creature in it, and therefore has been called the River Barrow, the ‘Boiling’ ever since.[6]

According to the Metrical Dindshenchus:

'No motion it made
The ashes of Meichi the strongly smitten:
The stream made sodden and silent past recovery
The fell filth of the old serpent.

Three turns the serpent made;
It sought the soldier to consume him;
It would have wasted by its doing the kine;
The fell filth of the old serpent.

Therefore Diancecht slew it;
There rude reason for clean destroying it,
For preventing it from wasting
Worse than any wolf pack, from consuming utterly.

Known to me is the grave where he cast it,
A tomb without walls or roof-tree;
Its ashes, evil without loveliness or innocence
Found silent burial in noble Barrow.[5]

This tale in the Dindshenchus indicates that the being slayed by Diancecht was a serpent named Meichi. Elsewhere the figure named as the slayer of Meichi is Mac Cecht.[5]

He made King Nuada a silver arm which could move and function as a normal arm. Later, Dian Cecht's son, Miach, replaced the silver arm with an arm of flesh and blood, and Dian Cecht killed him out of professional envy. Miach's sister, Airmed, mourned over her brother's grave. As her tears fell, all the healing herbs of the world grew from the grave. Airmed arranged and catalogued the herbs, but then Dian Cécht again reacted with anger and jealousy and scattered the herbs, destroying his daughter's work as well as his son's. For this reason, it is said that no human now knows the healing properties of all the herbs.[3]

Dian Cecht was also able to heal Mider after the latter lost an eye when struck with a twig of hazel.[7]